The metabolism of vitamin D has been studied and a variety of metabolites have been found. Prior to occurrence of their physiological activity, vitamins D are initially hydroxylated at the 25-carbon thereof in liver to give 25-hydroxyvitamins D, which is then hydroxylated at the 1.alpha.-, 24R- or 26-carbons thereof in kidney, thus transforming by metabolism into 1,25-dihydroxyvitamins D, 24,25-dihydroxyvitamins D or 25,26-dihydroxyvitamins D, respectively. Of these metabolites, the 1.alpha.,25-dihydroxy derivatives of vitamin D.sub.2 or D.sub.3 possess highest physiological activity and are considered as a final active product. Further, those active-type vitamins D are used as a remedy for the treatment of bone diseases, renal diseases, parathyroid disorder and the like. In recent years, there is a growing interest due to the discovery of new activities such as differentiation inductive or cell growth inhibitory action.
The active-type vitamin D.sub.4 to be sought by the present invention, i.e., (24S)-1.alpha.,25-dihydroxyvitamin D.sub.4 and the 24-epimer thereof, (24R)-1.alpha.,25-dihydroxyvitamin D.sub.4 are expected to possess an interesting pharmacological activity in association with the active-type vitamins D.sub.3 and D.sub.2. However, the above two compounds have not been synthesized for more difficulty in synthesis than the active-type vitamins D.sub.3 and D.sub.2.
Now, we have investigated the prior art process for the preparation of 1.alpha.,25-dihydroxycholecalciferol (1.alpha.,25-dihydroxyvitamin D.sub.3) by irradiation of 5,7-cholestadiene-1.alpha.,3.beta.,25-triol(1.alpha.,25-dihydroxy-7-dehydr ocholesterol) followed by isomerization (H. F. DeLuca et al, "Tetrahedron Letters", 4147 (1972) and H. F. DeLuca et al, "J. C. S. Perkin I", 165 (1979)), and have found that new (24S)-1.alpha.,25-dihydroxyvitamin D.sub.4 and the (24R)-epimer thereof are produced from new intermediates, 5,7-ergostadiene-1.alpha.,3.beta.,25-triol and the (24R)-epimer thereof.